As a result of the tightly packed atoms and strong bonds of the diamond lattice, diamond is the best conductor of heat known at ambient temperatures with high thermal conductivity. Of the many uses of diamond where its high thermal conductivity plays a role, the use as a heat sink, is probably the one which depends most directly on this property.
Polycrystalline diamond formed by chemical vapor deposition, herein sometimes called CVD diamond, offers the best potential as a heat sink. However, presently the thermal conductivity of CVD diamond differs from that of natural diamond in that it may vary through the thickness of a sample and is anisotropic. As discussed by M. Seal in the article, Thermal and Optical Applications of Thin Film Diamond, PHIL. TRANS R. SOC. LOND A (1993) pages 313-322, polycrystalline CVD diamond films show an anisotropy of thermal conductivity between directions parallel to (lateral) and perpendicular to the diamond film plane. The thermal conductivity measured perpendicular to the plane was found to be at least 50% higher than that parallel to the plane. The conductivity has been found to vary inversely with the growth rate and Raman line width. Since the diamond layers are heat spreaders, it is the parallel or lateral conductivity which is limiting.
It would be desirable to have synthetic diamond films with a structure that promotes high parallel and perpendicular thermal conductivity. It is further desirable to have a free-standing, polycrystalline diamond film that spreads large amounts of heat laterally at the surface that is used for mounting extremely closely packed electronic components. Likewise, it would be desirable to have a synthetic diamond heat sink that quickly dissipates heat generated by arrays of laser diodes.